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The Pharmaceutical Journal Vol 265 No 7114 September 16, 2000
Pharmacy Practice Research
Papers presented at the British Pharmaceutical Conference, Birmingham, September 10 to 13, 2000 pR67

Computer modelling of a dispensary supply service using discrete event simulation software

By D. Marriott, J. P. Scanlan* and D. Samways†

South West drug information and training, Bristol; *University of West of England, Bristol; †Cheltenham General hospital, Cheltenham

Introduction There are many forces of change currently acting on hospital pharmacy practice. The desires to improve clinical effectiveness, utilise new technologies and manage manpower shortages have generated much interest in the evaluation of existing and innovative pharmacy services. Effective comparisons of these services are difficult to perform, as they need to be comprehensive, representative, free from personal bias and independent of compounding factors. The understanding and co-operation of multidisciplinary staff is usually required and disruption to patients must be minimised and justified.
Inspection of pharmacy practice literature1 reveals the use of various evaluation methodologies and measures, often employed in combination. Some studies consider efficiency, or economic evaluation, others use patient satisfaction and/or preference of health care staff.
Manufacturing and retail industries widely use discrete event simulations to optimise the efficiency of their supply operations. The models provide rational and statistically valid representations of an organisation based on historical data. The latest products also provide clear animations of the systems, which are of value as presentation and training aids.
The aim of the current study is to use discrete event simulation software to model the supply function of a hospital dispensary.

Method The dispensary supply function at Cheltenham general hospital was defined by three flow charts: outpatient supply (OP), discharge supply (TTO) and non-stock inpatient supply (IP).
The following data (or estimates) were then collected:

  • duration of each step in the flow charts (means with ranges)
  • daily workloads (means with ranges)
  • per cent referrals due to incomplete, incorrect or ambiguous prescriptions
  • per cent items re-dispensed at final check stage
  • estimates of disruption due to phone calls
  • workload details, ie, types and numbers of items (means with ranges) per prescription
  • dispensary staffing details

The software package, Promodel, was used to create a model of the dispensary supply process from these data and estimates.

Focal points

  • There is much interest in the evaluation of existing and innovative pharmacy services
  • It is difficult to implement innovative pharmacy supply services without performing feasibility studies that can be time consuming and disruptive.
  • Other industries use computer-generated simulations to optimise the efficiency of their supply operations
  • Simulation software was used in the current study to model the dispensary supply function at a general hospital
  • The model can be used to optimise a multitude of organisational changes without the need to perform repeat feasibility tests

Results A representative simulation of a hospital pharmacy dispensary has been created using discrete event simulation software. Comprehensive statistical summaries of the supply processes have been produced that detail mean patient-waiting times, maximal capacity of the system and per cent utilisation of staff.

Discussion The model is currently being validated by comparing predicted supply times for IP, OP and TTO prescriptions with actual supply times as determined by the hospital computer tracking system.
Once validated, the model will be used to investigate a multitude of organisational changes, eg, staffing numbers and skill-mix issues, process reorganisations, and alterations to service priorities. These investigations can be achieved in a rapid, comprehensive, objective manner with minimum disruption to the function of the department.
Although modelling software will not replace feasibility studies, the application of this technology provides a highly effective tool for health care managers. Its use can help to ensure that only the most promising, optimised services are selected for feasibility studies.

References

1. Smith F. Evaluation of pharmaceutical services: (1) Objectives, designs and frameworks. Int J Pharm Pract 1999;7: 113-27.